1. Technical Field of the Invention
The present invention relates generally to the field of suspension systems, and more specifically, to an adjustable suspension system for a seat.
2. Description of Related Art
The ride quality and operator comfort of a work vehicle is adversely affected by vibrations or movement transmitted from the frame or chassis of the vehicle to the operator's cab. As the work vehicle travels across a surface, movement of the chassis induces the operator's cab to pitch, roll, and bounce. Movement of the cab can be particularly severe in agricultural and construction equipment vehicles because such vehicles typically operate on off-road surfaces or fields having a high level of bumpiness.
Operator comfort may also be adversely affected by the operation of various systems on a work vehicle. In particular, operation of various work vehicle systems can cause forces to be applied to the chassis of the vehicle which, in turn, are transmitted to the cab. Examples of these forces, which can cause the cab to pitch or roll, include the following: draft forces exerted on the hitch of an agricultural tractor by an implement (e.g., a plow); normal forces applied to a work vehicle as the vehicle turns in response to a steering device; clutch forces generated when a work vehicle clutch (e.g., a main drive clutch, four-wheel drive clutch) is engaged or disengaged; gear shift forces generated when a transmission of a work vehicle is shifted; braking forces generated as brakes of a work vehicle are operated; and acceleration forces generated when a speed actuator changes the speed of a work vehicle.
The movement of the cab caused by surface bumps and the operation of vehicle systems cause both qualitative and quantitative problems. An operator of such a vehicle experiences increased levels of discomfort and fatigue caused by the vibrations. Productivity is decreased when an operator is forced to rest or shorten the work day or is unable to efficiently control the work vehicle. The operator is also less likely to be satisfied with a work vehicle which provides poor ride quality. Under certain conditions, the frequency and magnitude of cab movement may force the operator to decrease driving speed, thereby further decreasing productivity.
To improve ride quality and operator comfort, work vehicles have been equipped with passive, semi-active, or active suspension systems to isolate the operator from vibrations caused by surface bumps. Such systems include vibration isolators mounted between the chassis and cab or seat. Passive systems use passive vibration isolators, such as rubber isolators, springs with friction, or viscous dampers, to damp vibrations, with different isolators used to damp different frequencies. Rubber isolators may be used, for example, to dampen high frequency vibrations, and air bags used to damp low frequency vibrations. Performance of passive systems, however, is limited due to design compromises needed to achieve good control at resonance frequencies and good isolation at high frequencies.
Semi-active systems achieve control and isolation between the chassis and the cab by controlling a damper to selectively remove energy from the system in response to movement of the cab sensed by sensors. Thus, in semi-active systems, the functional principle generally comprises modifying in real time the dampening of the suspension according to magnitudes, such as position, velocity, and acceleration, which are measured in real time by sensors placed on the suspension.
An active seat suspension system responds to motions of the vehicle by actively moving the vehicle seat in a direction and by an amount so as to compensate for such motions. Active systems use sensors to sense cab movement and a controller to generate control signals for an actuator, which applies a force to the cab to cancel vibrations transmitted to the cab by the chassis. The power needed to apply the force is typically supplied by an external source, such as a hydraulic pump. Unfortunately, hydraulic pumps, while common in the art, are associated with inefficiencies and high emissions.
A number of problems relates to the desirability of varying such things as the sensitivity and stiffness of the system. For certain conditions of operation it may be desirable to make the suspension system highly sensitive. At the same time, high sensitivity may not be desired for other conditions of operation, and particularly when an active suspension system is first turned on. It is preferable to allow the operator at least some time to become accustomed to the suspension system before a state of high responsiveness is entered. It is also generally desirable to be able to vary the rate at which the seat is moved in response to the sensor and, thereby, the stiffness of the suspension system. Different types of rides and bumpy conditions dictate different degrees of stiffness desired in the suspension system for optimum operator comfort.
Therefore, there is a need in the art for a seat suspension system that can be fully adjusted, and which, preferably does not implement a hydraulic pump. It is toward such a seat suspension system, and the manufacturing of such a seat suspension system, that embodiments of the present invention are directed.